Do ray sensors detect collision bounds?
Background

"Rays" are a method to detect if an imaginary line crosses one or more faces. That leads to the question: What faces?

In the BGE there are two kinds of faces:


visible faces (display mesh) and 
collision faces (physics mesh). 


These face types can but do not need to match. (Often it is better when there are less collision meshes than display meshes for faster processing).

Rays are part of the physics aspect. Therefore faces the physics would collide with are considered for hit detection.

Conclusion

I guess after this (hopefully understandable) explanation, you come to the conclusion that the ray will hit the shape defined by the objects Physics/Collision Bounds/Bounds


If it is set to Box, the physics mesh is a box where the display mesh fits in. 
If it is set to convex hull, the physics mesh will span a convex triangle mesh around the display mesh (faster than triangle mesh processing)
if it is set to triangle mesh, the physics mesh will match the display mesh (creates the most processing overhead)


Be aware: quads are broken into two triangles. The triangles might not match the triangles of the display mesh as there are two ways to break a quad.

You can see the current physics mesh by enabling Main menu/Game/Show Physics Visualization (the green mesh when resting otherwise white lines). 
Attention: The visualization on a convex hull is not necessarily correct. I guess it is simpler to detect collisions than drawing a convex hull.

Answer

The ray detects the collision bounds your explicitly set up.